Radio tuning system



Dec. 26, 1933. v w. H. HOFFMAN El AL 1,941,090

RADIO TUNING SYSTEM Filed April 14, 1930 3 Sheets-Sheet l m INVENTORS WH, HflFF/VA/V J]. H. MIX. BY 0' I 2%, I -4W J- M ATTORNEYJ Dec. 26, 1933. w. H. HOFFMAN El AL RADIO TUNING SYSTEM Filed April 14. 1930 3 Sheets-Sheet 2 M I 0 W +M ATTORNEYS W. H. HOFFMAN ET AL RADIO TUNING SYSTEM 5 Sheets-Sheet Filed April 14. 1930 5; m m w L T L j F h r A L A A A L n P Q J m? n wwd fi $3 c INVENTOR s 14/. H. HOFFMAN BY 3%, MIX

ATTORNEYS I of such systems.

* quency within said'band."

Patented Dec. 26, 1933 I ,RADIO TUNING SYSTEM William H. Hoffman, Bloomfield,N J.', and Donf ald H. Mix, Hicksville, N. Y., assignors to Burgess Battery Company, Madison, vllis a corporation of Wisconsi 7 g ApplicafimAPril14,1930. se ia -No. 444,1?!

'11 claims, (01.250

tuning elements. Thus, the short-wave receiver must be tunable over a frequency band which is abouteleventimes as wide'as the broadcast band, and yet it must tune more slowly'than the broadcast receiver due to the. crowding of amateur channels in the short-wave region.

This invention relates to systems for radio com munication, particularly to the receiving portion More especially the invention relates to radio receivers designed for reception of signals in the so-called short-wave" region em: bracing a relatively widerange offrequencies extending upward from about 3,000 kilocycles;

A primary object oftheinvention is to provide a unitary tuning mechanism for a receiver of the type specified which permits accurate tuning over a wide range of frequencies as compared to the tuning range of theusual broadcast receiver, such, for example, as'the short-wave regionextending from 3,000" to about 20,000 kilocycles, without the necessity for changeable inductance coils or any other alteration inside'the receiver.

It is a further object of the invention to provide a unitary tuning mechanism comprising a coarse tuning element which is continuously variable over the short-wave region and serves'to adjust a fine tuning element associated therewith to operate within a relatively narrow selected fre'' quency band, said fine tuning element being thereafter operable to select "a particular frepacity in shunt with a fixed inductance. This broadcast range. But whereas inthe broadcast riable capacity operating betweencertain maxiband of 500 to 1500 kc., tuning over the shortof frequencies to be covered.

Other objects are to provide a radio-frequency amplifier or a complete radio receiver which is continuously tunable at a relatively slow rate of frequency change over a wide range in frequency as compared to the usual broadcast receiver; as 7 well as to provide a short-wave "adapted for adapting any standard broadcast receiver to operate over the short-wave region. g

If desirable, the tuning mechanism may be designed to provide substantially straight line fre-' quency tuning over the entire tuning range.

In the'design of a radio receiver suitable for short-wave "reception certain problems must. be solved which are not encountered in receiver design for the ordinary broadcast range; In the first place, whereas the broadcast region covers" the relatively narrow frequency band extending from about 500 to 1500 kc., the short-wave region at present extends from 3,000 toabout 20,000 kc In the second place, the close allocation of broadcasting frequencies within the short-wave region necessitates the use of a receiver which is highly selective over the entire frequency-spectrum and hence one in which the frequency of tuning varies at a relativelyslow rate with adjustment of the Loci-dance with the equation comes about 45 1.

tations, it will ,be obvious, that to provide a single 'ble condenser. to permit tuning over a small 'portion of the short-wave region, sufiicient coils- 0f. successively increasing inductan'ces being thus provided to coverthe entire short-wave band. But here again. furtherdifficultiesare immedition of its iminimum V and maximum capacity As regardsthe tuning adjustment of the re-' ceiver, experience has taught that most satisfac- I tory'tuning is obtained by use of'a variable caapplies to short-wave tuning as well as the usualwave band is not-so simple, due to the wide range 1 capacity: capable-of tuning'satisfactorily over the r entire short-wave region would be impracticable.

Accordingly, ithas been the practice iniconstructing short-wave receivers to provide a-mul:- i tiplicityof plug-in .type inductances, each adapted 1; s when connected in shunt with a. standard varia-' ately encountered. Since as pointedout, the tun ing range covered by a given condenser. is a func-,

range it isafairly simple matter by the use of a singlefixed inductanceshunted by a single vaf 53)? mum :and minimum capacity values to obtain a v tuner which will tune over-the entire broadcast squareroot of the tuning capacity. "Or, -exp ressfed in a slightly different manner, the maximum and minimum resonance frequencies are related to the correspondinglimiting'yalues of capacity in ac- Inthebroadcast range this ratio-amounts to only 9:1;whereas, oven-the short-.wave region it be- Inasmuch asthe minimum capacity of a condenser is in general beyond con-r trol, being determined by certain physical limi- I values, when a variable condenser of the ordinary type is used one always runs into the difficulty of unequal frequency span between the high and low frequency ends of the receiver range. A condenser which is small enough to tune nicely at 15,000 kc. will tune unnecessarily slowly at 3,000 kc., and furthermore requires the use of a large number of plug-in coils because of the successively smaller ranges covered by the condenser as the receiver is adjusted to lower'frequencies. In case the tuning condenser is made large enough to tune satisfactorily at 3,000 kc., only a few plug-in coils will be required, but as the receiver is adjusted to the higher frequencies, the frequency coverage will become so great that successful tuning of a sharp signal will become almost impossible.

By way of example, suppose a condenser to be selected having its maximum to minimum capacity in the ratio of 9:1; such a capacity will cause a frequency variation of the order of 1:3. With a given coil connected in shunt it may be assumed that at the initial capacity setting the frequency of tuning is 1,500 kc. The capacity being increased to its maximum value the frequency of tuning will be reduced to 500 kc. The difference is 1,000 kc. With a different coil the tuning frequency at minimum capacity setting may be assumed at 15,000 kc. An increase of capacity to its maximum value will reduce the resonant frequency to 5,000 kc., a difference of 10,000 kc. In other words, with each different coil, equal displacements of the adjustable element of the condenser produce unequal changes in the tuning frequency, and thus the speed or rate of tuning is said to be different. The greater the frequency change for a given change in capacity, the higher is the rate of tuning. When the rate of tuning is high it is, of course, difficult to tune accurately, since a very slight adjustment of the tuning element will effect a material change in frequency.

The present invention provides a tuning device for short-wave tuning which overcomes all of the aforementioned difficulties and in addition embodies added desirable features. The specific tuning system disclosed covers all frequencies from 3,000 to 20,000 kc. without the use of plug-- in coils or the necessity of any other alteration inside the receiver. This has been done without sacrificing the sensitivity of the receiver. At no place over the entire frequency range does the tuning speed or rate of tuning exceed a range of substantially 1,500 kc. per 180 dial movement of the fine tuning element so that the system tunes in substantially the same manner as present-day broadcast receivers. Furthermore, over the entire tuning range extending from 3,000 to 20,000 kc. the tuning is exceptionally close to straight-line frequency tuning.

Broadly speaking, the invention accomplishes the above mentioned objects by providing a tuning mechanism consisting of coarse and fine tuning members arranged to cooperate in a certain manner. The coarse tuning member is a resonance circuit comprising variable inductance and capacity elements in parallel electrical connection. The fine tuning member is connected in additive electrical relation to the device of similar. character in the coarse tuning member. That is, if the fine tuning member is a capacity, it is connected in parallel with the capacity of the coarse tuning member, whereas if it is an inductance, it is connected in series with the inductance of the coarse tuning, member.

The fine tuning member comprises two cooperative movable elements, the first being independently movable for fine tuning, the second being positively mechanically controlled by the control adjustment of the coarse tuning member. The

. reactances of the coarse tuning member are thus adjusted conjointly with the second element of the fine tuning member. This positive relation between positions of coarse and fine tuning elements makes it possible to so design the latter that for all settings of the coarse tuning member, the frequency ranges covered by movement of the fine tuning member from minimum to maximum setting will be approximately equal.

In the specific embodiment of the present invention the tuning device is composed of three separate items all mounted as a single unit, preferably on a small panel of insulating material. It comprises an inductance in the form of a small variometer. In shunt with the variometer is a midget or micro type of variable capacity of about 135 micro-microfarads maximum capacity. In shunt with this capacity is another variable capacity of special design in which both rotor and stator plates are movable. The operation of the device in general is as follows: The variometer and micro condenser tune the circuit to approximately the desired frequency while the special condenser acts as a Vernier capacity of variable maximum to minimum capacity ratio and tunes over the desired band.

A uni-control device is provided for simultaneously adjusting the variometer, the micro-condenser and the stator plates of the special condenser, the latter operation being required to select the proper maximum to minimum capacity ratio for the special condenser to permit tuning over the desired frequency band based on the rough tuning adjustment. This may, of course, be accomplished by mounting all of the elements in question upon a common shaft, or as is disclosed specifically in the present instance, by linking the shafts of the various elements together by means of a system of belts and pulleys. This arrangement constitutes a shift dial arrangement by means of which the operator may shift to any one of 13 overlapping frequency bands at will within a fraction of a second, thereby covering theentire short wave region. The rotor plates of the special condenser are turned by the second dial which constitutes the usual tuning control for selecting a desired frequency within a given band. The plates of the special condenser are so designed that whatever the position of the shift dial the frequency range covered by adjustment of the rotor plates remains substantially constant at about 1500 kc. per band.

As embodied in a radio receiving system, the variometer may be provided with a stationary tickler winding for regenerative purposes. It is a feature of this arrangement that the necessity for wide variation in oscillation control often found in short-wave receivers of wide tuning range is practically eliminated, since the coupling between the variometer windings and the tickler automatically increases or decreases respectiv ly as the inductance of the variometer nears its maximum or minimum. values.

The special condenser is so designed that for any position, of. the stator plates, adjustment of the rotor plates through an angleof 180 will adjust the tuning frequency over a band of substantially 1500 kc. This result is obtained by carefully shaping both the rotor and stator plates to cause the interleaving area to be varied in ac- .cordance with the setting of the stator plates well as in accordance with the position of the.

rotor plates. The proper proportioning of therotor and stator platesis obtained from acone I; sideration" of the fact po'inted'out above that the the ratio varies between .these two elements.

of variometer A is -shown. V

Figured shows in circuit diagram. forman ap- From this data it is possible to'calculate if it be desired to cover a frequency range .of 20,000 to 3,000 kc. in steps of. 1,500 kc., that the tuning con- V I V 1 screws 11 with shafts S parallel and in such mandenser must have a variable ratio of its minimum to maximum capacity such that the ratio may be set at any desired value between theelements (1.08) =1.166 and (1.50) =2.25.

-Inorder that a fair value of ,inductance'may :be. used for thevariometer, the special condenser sag; frequency end mustcause relatively large areas of rotor and stator plates to become interleaved. This is accomplished, of course, by suitably shaping the rotor and stator plates, and by providing means for shifting the interleaving portion of the stator as compared to the rotor plates.

Since it is' undesirable both from the standpoint of mechanical simplicity and electrical efi'lciencyto use a small inductance and cover the entire frequency range by means of a large capac-.

ity, use'has been made of the variometer in order to insure thatregardless of the portion of the frequency band over which the set is being operated, there is a fair proportion of inductance to-capacity. in the circuit.

' Likewise, it is desirable to have a certain,

amount'of minimum capacity in the circuit when Working at the lower frequencies whereit is pos sible to use it. This is supplied by means of the micro condenser in shunt with the variometerf 1 Having thus described the invention in general terms, reference-will nowbe had tojthe drawings for a'detailed description of a specific embodiment thereof which has proved highly satisfactory in actual practice for short wave reception;

, 7;; Referring tothe drawings, Figure 1 gives a plan view showin the assembly and mechanical details of atuning device in accordance with the present invention. 1

Figure 2 shows a side elevation as viewed from,

c To avoid confusion, the fragments of condenser C which are visible, are.

the right in Figure 1.

omitted, i

Figure3 shows a section along the line 3-3 in Figure 1,except that a midsectionof the stator plication of .the inventionwhich may be utilized as a short-wave receiver or asan adapter for adapting the usual type of broadcast receiver to short-wave reception. Figure 5 shows in circuit diagram form'a com plete multi-stage short-wave receiving" system wherein the tuning is accomplished'by: means of thespecial tuning ,device of thepresent inven- ..tion. i. i 1: V

' plates.

*' Like elements are severalv views.

Referring moreespecially toFigures 1-3, inclusive, the tuning mechanism comprises the variometer A, microi, condenser Bland-the special condenser C, all suitably'mounted upon asingle panel 1 of insulating material. i The special condenser 0 comprises two complementary units R1 and R2, each consisting of a set of condenser plates N mounted upon a shaft Srotatablysupported within a'housing 3 upon I journal bearings 8 afiixed to conductive end plates 5 which latter'are suitablyipositioned in rigid assembly and spaced relationby means of spacing members 6 and screws '7. Lock nuts 4 maybe provided to'longitudinally adjust the condenser The unitsRi and tweenin'sulating members 9 and 10 by means of R2 are rigidly mounted besimilarly designated in the v nor as to permit interleaving of plates N1 of unit R1 with plates N2 of unit R2. Conductors 12 may be added to insure positive electrical connection between the shafts S and end plates 5. The units R1 and R2 are, of course, insulated from each other due to mounting between the insulating members 9 and 10. i

It is usually preferable tolimit the angular movement of platesN to. 180, and to this end each shaft S is provided with a pin 13 adapted to engage stops 14 and 15 (see Figure 3) affixed to end plates 5. The condenser structure is mounted upon panel 7 l by means of spacing members lfi and bolts 17.

Shaft S2 extends through the panel being fitted at its outer end with a pulley P1 of insulating material for purposes explained below. Shaft S1 likewise extends through panel .1 and also through a second panel 18 which constitutes a portion of a cabinet in which the structure is. housed, the

It will be observed: Figure Bthat the condenser plates of units R1 and R2 are soshaped that for a given setting of unit R2 therotation' H of unit/R1 counter'clockwisebetween stops l4 and 15 will produce a gradual increasein the interleaving area of plates N1 and N2 thereby producing a variation of capacity which changes from a certain minimum to a certain maximum value. It will be observed further that successive adjustments of plates N; in a clockwisensense afford successively increasing maximum interleaving areas between plates N1 and N2 thereby increasing the ratio of maximum to minimum capacity of the condenser. Itl willv thus. be seen that by suitably positioning the condenser plates N2 corresponding to a frequency band over which it is a desired to tune, that the same speed of tuning due, to adjustment of dial D maybe obtained over a frequency band of given width such as 1500 kc. irrespective of the allocation of the band within the short-wave region.

The unit R2 corresponds. tothe stator element .of the usual variable condenser whilethe unit R1 corresponds to the rotor element. "Ihe"stator unit R: is in this instance variablein order to permit adjustment of the ratio of maximum to minimum for a movement of plat-esNl.

The micro condenser B also mounted upon the panel 1 comprises a set of statorplates 35 is ailixed to the frontof panel 1 by means of an externally threaded bushing 3'7 which passes through the panel being held in place by means of a lock nut in the manner well known in the art. A pulley P2 is mounted upon the outer end of rotor shaft S3 of condenser E which shaft projects through the panel 1.

The variable inductance or variometer A consists of a coil 20 rotatably mounted within stationary coil 21. The stationary coil 21 is mounted, as shown more clearly in Figures 2 and 3 upon the inner periphery of a ring 22 of suitable insulating material. The movable coil is wound upon a second ring- 24 of insulating material which is rigidly mounted upon shaft S4 whereby rotation of the shaft produces angular displacement of coil 20 relative to coil 21. Pulleys P3 and P4 are fitted to the portion of shaft S4 projecting through panel 1, while a dial D2 is affixed to the outer end of the shaft which projects through the cabinet panel 18. This dial likewise cooperates with a stationary indicator affixed to the panel 18 whereby the position of adjustment is indicated.

j A belt 27 extends over pulleys P1 and P3 being aflixed thereto respectively by means of screws 28 and 29 to provide a positive drive. Likewise a belt 30 passes over pulleys P2 and P4 being affixed thereto respectively by means of screws 31 and 32 to provide a positive drive. It will thus be seen that adjustment of dial D2 simultaneously varies condenser unit B, the variometer A and the stator element R2 of the special con denser C. On the other hand, adjustment of dial D1 varies the position of the rotor element R1 of the special condenser C independently of the position of the stator element S.

The external electrical connections of the various elements are not shown in Figures 1 to 3, but are shown in the circuit diagram drawings of Figures 4 and 5.

Coarse tuning to select the frequency band of 1500 kc. within which it is desired to select a particular frequency is accomplished by adjustment of dial D2. By means of the pulleys and belts heretofore described, the adjustment of dial D2 causes motion to be transmitted to shaft S2 of condenser C and shaft S2 of condenser E, the variorneter A, of course, being directly operated. In this manner the variable elements thus connected together are caused tomaintain a predetermined established relationship in all conditions. Having selected the frequency band within which it is desired to tune. by adjustment of dial D2, the particular frequency to be selected within the band is then obtained by operation of dial D1 which provides the fine tuning adjustment by means of rotor unit R1. The predetermined established relationships between the positions of the movable elements of reactances A and B and shaft S2 of condenser C, make it possible to so design the reactances, as will be explained hereafter, that for all settings of the coarse tuning member, equal angular displacements of the fine tuning member R1 cause substantially equal changes in the resonance frequency of the tuning mechanism.

Straight line frequency tuning of circuits comprising inductance and capacity are built on the general principle expressed in the following equation, which is chosen arbitrarily to cover the case where frequency decreases as angularity in- Where L and C represent the inductance and capacity corresponding to an angular adjustment 9 of the tuning element from its initial setting at which the inductance and capacity values are Lo and Co respectively. If the adjustment of the tuning element is such as to vary the capacity only the equation reduces to the simpler form:

Both inductance and capacity may be caused to vary together to meet the conditions represented by the Equation (2) but the usual practice is to vary the capacity only in accordance with Equation (3). To cover the short-wave frequency range by means of a single tuning circuit having straight line frequency characteristics either the capacity and inductance would have to assume excessive size, or the tuning would be too rapid for accurate adjustments at any point. The present invention overcomes such objection.

The shape of the plates N1 of the fine tuning .member of the special condenser C resemble somewhat the shape of ordinary straight-line tuning condensers, and are designed upon the consideration stated that in a resonant circuit with the inductance remaining constant, the resonance frequency varies inversely as the square root of the capacity. Considering therefore a single setting of the coarse tuning dial D2, the special condenser must have its plates N1 so shaped that the square root of the capacity of the entire system varies inversely as the angular displacement of the fine tuner control dial D1.

The shape of the second set of plates N2 must be such that as the coarse tuner dial D2 is moved to lower frequency settings, a greater maximum surface area is presented to plates N1. The plates I are further so shaped that at the lower frequency settings of plates N2 the rate of change of interleaved surface of plates N1 and N2 is more rapid for equal angular displacements of the fine tuning member than it is at the higher frequencies. This increased rate of change of interleaved surface at the lower frequencies is obtained largely by increasing the width of the stator plates N2 toward the low-frequency settings in such manner that upon advance of plates the use of the same set of dies for both sets of plates, thereby simplifying and reducing the cost of manufacturing operations. However, from Equation (3) above it is readily appreciated that plates N1 and N2 may take a variety of shapes dependent upon the design of the inductance and capacity of the coarse tuner, as well as upon the consideration that either of them may be maintained constant during coarse tuning.

It will also be noted that with plates N1 remaining in their initial position, as shown in Figure 3, movement of plates N2 from their initial setting causes some interleaving of the two sets of plates. In the position shown, plates N2 are at their mid-setting but the area interleaved is very slight. This area. increases as plates N2 are wouldbe rendered difficult due to the eflect of moved'angularly in. a. clockwise directiom but a r i' If the circuit of Figure 4 is to'be embodied in -a-complete radio'receiver, terminals E1, E2 and 1E3 are'connected 1 respectively toterminals F1-,

even at vtheir final setting, it is not considerable. In fact, the capacity changes due to the interleaving caused by movement of platesN'z are practically negligible when compared with the capacity of micro condenser B atcorresponding settings and ordinarilyineed not be taken into account in the design of the-mechanism.

sign the tuning mechanism that movement of plates N2 from their minimum setting causes appreciable interleaving with plates N1 and the capacity changes caused thereby may be considered as assisting in the coarse tuning and taken into consideration when designing the coarse tuner; that is, plates N2 may thus become apart 'of'the coarse tuner.

To simplify construction, the coarse tuning elements may, of course, all be mounted upon a common shaft, in which case the pulleys and belts could be omitted; For example, the rotor elementof'co'ndenser B and the movable coil 20 of the variometer A could all be mounted upon an extension of shaft S2 carrying the stator plates Nzof the special condenser.

To further simplify construction it might prove expeditiousto'combine the special condenser C and the micro condenser B into a singlecon denser which would be similar to condenser C except that the plates thereof would have additional interleaving surface to supply the capacity i furnished by condenser B, which additional sur face could be arrangedto be brought into operation by manipulation of the coarse tuning 'control. i I The circuit diagram'of Figure 4 illustrates the manner in which the short-wave tuner of the present invention may be'embodied in a radio receiver, or inasho'rt-wave -adapter for adapting an ordinary broadcast receiver toshort-wave receptionf The tuning "mechanism is; enclosed within the dottedrectangle T wherein it will be 7 obvious that the "variometer, special condenser and Vernier condenser are connected in parallel electrical relation; 1 The dashed lines L indicate the uni-control feature whereby the coarse'tune ing adjustment is obtained; while the lower plates of the specialcondenser C are indica'ted as being tuning adjustment. v i

The input circuit of the tuning deviceT is connected at its" opposite terminals through a condenser, 42 to antenna 43'and to emana e respectively;. Theoutput terminals'of the tuning element are connected througha' gridcondenser independently variable to aczcom'plish the fine and leak resistance 45 to the grid, electrode and, to the cathoderespectively of avacuum tub'eLY which in this instance is indicated as beirig of v the heater element type. a i o I ,It was previously stated that pulleyPi isfof insulating material. The reason for this is ap -1 parent from Figure 4 wherein it is to be noted that pulley P1 controls unit R2 of the special condenser which is connected tothe high potential side of the. tuning circuit. If the fine tuning element R1 were connected tothe grid electrode of tube V'instead of the statorelement R2, tuning s'istance 56 may also be included topermit adbody capacities. o

' F2 and F3 whereby a source of current 47 is applied to'the heater element of tube V, and headphones 48 anda space current supply source 49 the detector tube socketoi the broadcast receiver. With such an arrangement the radiofrequency waves impinging upon the antenna 43 are selected and detected by means of the circuit of Figure 4, and are then passed through thefcontacts of plug '51 to the detector output circuit of the broadcast receiver and thence through the audio-frequency stages thereof to the receiving element. With such an arrangement the broadcast receiver, of course," supplies the necessary. heating current and space supply current for operating the tube V of the adapterucircuit of Figure 4. With the broadcast :receiver connected to the adapter circuit in: this manner, the radio-frequency stages of the broadcast receiver are, of course, ineffective due to the fact that the lead which normally extends to the grid electrode of the broadcast receiver detector tube is open.

For greater practical success, refinements may be included in the circuit of Figure 4. For ex-" arnplalthe output and input circuits-oi the detector tube V may be regeneratively coupled as by means of the tlckler .coil 52 placed in inductive relation with the variometer A. The condenser 53 and variable resistance 54 in series may be connected acrossthe output'circult of the detector tube to control regeneration. "A radiofrequency choke coil 55 may betserially interposed in the plate circuit toichoke out theradiofrequency currents therefrom, and variable rejustment 'ofthe plate voltage-in which event it is 1 desirable to shunt the resistance with a con-' denserl57in order to reduce 'electrical disturbanccs resulting from adjustment of the resistance. V s a Figureb shows diagrammatically a complete i short-wave receiver employing a unitary tuning device (TL inacc'ordance with the presentinvenble. The detector output is connected through two stages of audio-frequency amplification comprising transformers P1 and" P2, vacuum tubes V3 and V4 to a pair of headphones or other receiving element 40. s r

Battery B1 which may be tapped at suitable potentials serves to provide space current for the several tubes, and also a suitable potential to the screen-grid of tube V1; The filaments of the tube V1.

Capacities 65v serve to bypass high frequency currents in the well-known manner in order to prevent undesired coupling effects tending to produce sustained oscillations. Capacities 66 serve to bypass the high-frequency currents around the primary winding of transformer P1, thereby preventing the radio-frequency currents from entering the audio-frequency stages.

A uni-control element L1 may be provided as indicated by the dashed lines for simultaneously adjusting the variometer A, stator unit of the special condenser C, and the vernier condenser B of both tuning elements T1 and T2 in order to provide the rough tuning adjustmentfor the entire receiver. To the same end the rotor element R of the. special condensers C may be mechanically coupled, as: indicated by dashed line L2, to provide gang tuning for the fine tuning adjustment. The, tickler coil 52, resistance'56, and capacity 57: serve the same functions as the like designated elements in Figure 4.

The tickler coil 52 may be convenientlyand advantageously mounted beside the stationary coil 21 of variometer A upon the inner periphery of the insulating ring 22. In addition to the mechanical simplicity afforded by this arrangement there is the additional advantage referred to. above that the coupling between tickler coil and variometer is automatically varied in accordance with the variometer adjustment to provide an approach to. optimum coupling at all times.

A brief explanation of a procedure suitable for designing our improved tuning mechanism by those skilled in the art may be of assistance in understandingthe invention. The desired frequency ranges ofboth. the coarse and: the fine tuners may be arbitrarily chosen and the maxi-- mumand minimum values of the reactances of point of; each such section. An approximate shape for the independently movable plates of the fine tuning membercan be estimated roughly by remembering that interleaved area is a direct function of capacity and that the total capacity of the system must vary as. the square of the angular displacement of the tuning control from :its initial position. The rate of increase width of the plates operated conjointly with the coarse tuning member must be a matter of trial and errorunless one wishes tocompute the actual.

capacity and inductance conditions, of the coarse tuning member necessary for itsevery position. With the coarse tuning member in an arbitrary position, preferably the minimum, point of one of the heretofore desc ibed sections, the fine tuning control may be; moved through 180 and the valuesof: resonance. frequency plotted. against angular displacement. not a straight line, trial and error changes in the .shape of the independently movable plates may be made until the curve becomes substantially If the resulting curve is straight. Then if the frequency difference between initial and final setting does not equal that desired, the Width of the plates movable conjointly with the coarse tuning member may be varied until such desired frequency range is secured.

A new position of the coarse tuning member may then be chosen. The relation between angular displacement and frequency may be a substantially straight line but the width of the con jointly movable plates will probably have to be i changed in the new portion which is now being interleaved in order to secure the desired frequency rangefor the finetuning member. This procedure may be repeated until the entire range of the tuning mechanism has been covered. In the present invention both sets of plates of the fine tuning member are of the same shape. This requires more than ordinary care in the design of the plates of the fine tuning member and renders the design considerably more difficult, but, as was explained heretofore, that is not necessary, and the procedure outlined above will secure substantially straight line frequency characteristics throughout the entire range of the tuning mechanism. The relation need be only approximately a straight linesince it is the primary object of the invention to secure slow and accurate tuning at the higher frequencies.

Although there has been described and illustrated but one embodiment of our invention, it will be apparent to those skilled in the art that many variations therefrom are possible within the contemplated scope of our invention. For example, the fine tuning member may be an inductance instead of a capacitance. Such an inductance would then be connected in series with variometer A to secure an additive relation between their inductive reactances. It is also appreciated that additive relation need not be maintained between the fine tuning device and the, device of similar electrical character in the coarse tuning member. For instance, condenser 0 might be connected in series with condenser E. Such an arrangement, however, would, unnecessarilycomplicate the design of the tuning mechanism.

What is claimed is:

1. A radio tuning mechanism tunable over a wide range in frequency, at a relatively slow rate of frequency change with adjustment of a tuning element thereof, comprising coarse and fine tuning members, said coarse tuning member comprising a resonance circuit tunable by a single coarse tuner control and including inductance and capacity at least one of which is variable, the

fine tuning member comprising a variable tuning,

device included in said resonance circuit and comprising two movable elements, one said element being independently adjustable for providing fine tuning over a relatively narrow band width, the other said element being movable by said coarse tuner control for causing said fine tuner to tune over a relatively narrow band width for all settings of said control.

2. A unitary radio tuning mechanism tunable over a wide range in frequency at a relatively slow rate of frequency change with adjustment of a tuning element thereof, comprising coarse and fine tuning members, said coarse tuning member comprising a. resonance circuit tunable over said -frequency range bya coarse tuner control, said resonance circuit including inductance andzcapacity at least one of which is variable, said fine rotary interleaving plate type connected in shunt with said capacity and consisting oftwo sets of plates mounted on separate shafts, a first set beingindependently adjustable to provide fine tuning over a relatively narrow band width, the

plates of said set being shaped to vary the reso- '.nance frequency of said circuit insubstantially equal increments for equal angular adjustments of saidplates, theother set of plates being mov able by said coarse tuner control and shaped to so vary the ratio of maximum to minimum capacity due to adjustment of said first set as to permit said first set to tune over a relatively narrow band width for all settings of said coarse tuner control.

- 3. A slow-speed, wide range radio tuning meche anism comprising coarse and fine tuning members in combination, the coarse tuning member comprising inductance and capacity devices, at least one of which is variable, the fine tuningmember comprising a variable tuning device in additive electrical connection with the device of similar 1' changes in a frequency characteristic of the tuning mechanism.

4. A radio tuning mechanism tunable over a wide range in frequency at a relatively slow rate of frequency change with adjustments of a tuning element, comprising coarse and fine tuning members in combination, the coarse tuning mem ber comprising a resonance circuit including inductance and capacity devices, tunable by a single control over said frequency range, the fine tuning member comprising a variable tuning device in additive electrical relation with the device of similarcharacter of said coarse tuning member, said fine tuning member comprising two movable elements, the first of said elements being independently movable for fine tuning, the second of said elements being movable by the control of said coarse tuning member to so control the electrical relations between said first and second elements that, for all positions of said coarse tuning member, equal mechanical adjustments of said first element produce comparable changes in resonance of said circuit.

5. A radio tuning mechanism tunable over a wide range in frequency at relatively slow rate of frequency change, comprising in permanent unitary assembly, coarse and fine tuning members in combination, said coarse tuning membercomprising a resonance circuit tunable by a single control over said frequency range and including inductance and capacity, the fine tuning member comprising a variable condenser in parallel electrical relation with said capacity, said condenser comprising two movable elements, the first element being independently movable for fine tun- -ing, the, second element being movable by the control of said coarse tuning member to effect positive relation between the positions of the two, saidrelation together with the shapes of said elements cooperating to cause equal displacements of said fine tuning element to effect comparable changes in the-resonance.frequency of said tuning mechanism for all positions of said coarse tuner control. tuning member comprising a condenser of the over'a wide range in frequency, comprising coarse and fine-tuning members in combination, said coarse tuning member comprising a resonance circuit including an inductance and capacity in parallel connection, tunable over'said frequency range by a single control, the fine tuning member comprising avariable condenser in parallel,

6.- A radio tuning mechanism tunable. at comparable rates of frequencychange at all points:

connection, with said capacity, said condenser comprising two adjustable elements, the first element being independently movable for fine tun- Y ing,the second element being movable by'the control of said coarse-tuning member to vary the capacity relations with respect to said first element, said relations, together with the shapes of said elements cooperatingin a manner such that, for allpositions of said coarse tuning member, displacement of said fine tuning member from-minimum to maximum setting covers coma parable frequency bands. I

'7. A radio tuning mechanismtunable at a relatively slow rate of frequency change over a Wide range in frequency, comprising coarse and fine tuning members inicombination, said coarse tuning member comprising a resonance circuit including the usualinductance and capacity elements tunable over said frequency range by a single coarse tuner control, the fine tuning member comprising a variable condenser in parallel electrical relation with said capacity, said con-I denser comprising two movable interleaving sets dependently movable for fine tuning, the second set being movable by the control of said coarse tuner, the relative positions of said coarse tuner elements and said second set of plates being adjusted so that for all settings of said coarse tuner control, equal displacements of the control of the fine tuning memberproduce comparable changes in the resonance frequency of said tuning mechanism. a q 8. A radio tuning mechanism tunable at all points over a wide range in frequency at comparable rates of frequency change comprising, coarse and fine tuning members in combination, said coarse tuning membercomprising a resonance circuit including inductance and capacity elements, tunable over said frequency range by a coarse tuner control, the fine tuning member comprising a variable condenser in parallel elec tricalrelation with said capacity, said condenser comprising two movable interleaving sets of substantially J-shaped plates'mounted in opposition upon separate shafts, the-first set being independently movable for fine tuning, the second set being movable by the control of said coarse tuner, the relative positions of said coarse tuner elem'ents and said second set of plates being so adjusted that, for all settings of said coarse tuner control, equal angular displacements of said first set of plates produces comparable changes in the resonance frequency of said tuning mechanism. w

9. A radio tuning mechanism tunable vat a substantially uniform rate over a wide range in frequency comprising coarse and fine tuning members in combination, said coarse tuning member comprising a resonance circuit including inductance and capacity elements at least one of which is variable, the fine tuning member:

comprising a condenser having two movable in- 1 H) of similarly shaped plates, the first set being interleaving plate elements, the first of said elements being independently movable and so shaped that, in its cooperation with the second element, there is a substantially straight line relation between the angular displacement of said first element and the resonance frequency of said tuning mechanism, the second element being operatively connected with the control of said coarse tuning member and being of such shape that, for all settings of said coarse tuning member, displacement of the fine tuning member from minimum to maximum setting covers substantially equal resonance frequency bands.

10. In a radio tuning mechanism capable of tuning within a frequency range of from 3,000 kilocycles to 20,000 kilocycles, permanent coarse tuning means having fixed and movable elements, and fine tuning means in cooperation, said fine tuning means comprising two sets of interleaving rotatable plates, the first set being movable conjointly with the movable elements of said coarse tuning means, the second set being independently movable, said plates being so shaped that, for all positions of said coarse tuning means, equal displacements of said fine tuning means causes substantially equal changes in the resonance frequency of said tuning mechanism.

11. In a radio tuning mechanism capable of tuning within a frequency range of from 3,000 kilocycles to 20,000 kilocycles, the combination with a coarse tuning means having fixed and movable elements, of a fine tuning means comprising a variable condenser having two sets of interleaving rotatable plates, one set being movable conjointly with the movable elements of said coarse tuning means, the second set being independently movable, said plates being substantially J-shaped and so proportioned that for all positions of said coarse tuning means, equal displacements of said fine tuning means causes substantially equal changes in the resonance frequency of said tuning mechanism.

WILLIAM H. HOFFMAN. DONALD H. MIX. 

